Many paints are customarily available in pasty form. Mixing paint of a particular color is generally done by eye. This is a satisfactory process for small scale work such as, e.g., making an oil painting, but it is unsatisfactory for many graphic arts and commercial purposes, particularly if a match to a particular color is desired. Even though in the hands of a skilled person, a close match may be obtained, an exact match is very difficult to achieve, particularly having regard to the fact that the color or the wet paint is different from the color of the paint when it is dry, particularly with water-based systems.
Even if the user is assisted by some sort of mixing or formulation guide, he or she has no easy and accurate method of measuring the relative volumes of material necessary and subsequently mixing them evenly to give the desired final color. U.K. Specification No. 2106794 purposes a system for measuring accurately small quantities of viscous colored liquids for use in paint formulation, but such a system is impractical for doing color formulation. It is effectively useful only for tinting white or natural bases to alter the color slightly.
The problems referred to above are compounded in the case of color matching or color proofing systems in which it is desired not only to produce a given color, but also to produce a specific mixed volume of that color, e.g., sufficient to cover a proofing sheet completely but without leaving any material excess and without incomplete coverage at any point.
We have now found that the disadvantages noted above may be avoided and accurate formulation of pasty materials obtained using a sequential extrusion technique as explained below.